In many external-rotor motors, the shaft of the external rotor is supported in a so-called bearing support tube on whose outer side a stator lamination stack is mounted. The shaft is usually mounted on the hub of a so-called rotor cup, and is supported within the bearing support tube by means of bearings, e.g. sintered bearings or rolling bearings. The type of bearing system depends principally on the desired service life of the motor and the desired smoothness.
For installation of the shaft, the bearing support tube usually has, on its side facing away from the rotor cup, an opening where components are located that serve to retain or support the shaft, e.g. a thrust bearing, spring member, retaining washer, bearing cover, or the like. Dirt can penetrate through this opening and shorten the service life of such a motor. Time is also needed for assembly, making such motors more expensive.